You can't cleanse it off, unless the new patch that buffed summoners changed that.
If you havn't seen faker's 1v1 zed highlight, he uses skill but also he had QSS, thats how he wonhttp://www.youtube.com/watch?v=da09LgzA0sY - go look.
As for cleanse, im almost 99% sure it doesn't cleanse zed ult.

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